The present invention relates to an image sensing apparatus and, more particularly, to a high-resolution image sensing apparatus using an image sensor such as a charge coupled device (CCD).
A recent advance of image sensors such as a charge coupled device (CCD) has achieved a high image quality, a low price, and a small size of image sensing apparatuses, e.g., household compact video cameras and still video cameras. Consequently, a satisfactory image quality can be obtained by a television standard of, e.g., NTSC. In addition, camera shake correction is currently performed in video cameras and the like, and this further improves the image quality of dynamic images.
A camera shake is a phenomenon in which photographed images move vertically or horizontally while a user is performing photographing by holding a video camera in his or her hands, since the hands or the body of the user slightly moves independently of the user""s intention. Images thus photographed give a viewer a considerable uncomfortableness when reproduced on a television monitor or the like.
To avoid this camera shake phenomenon, conventional video cameras make use of, e.g., a variable angle prism (to be referred to as a xe2x80x9cVAPxe2x80x9d hereinafter).
A practical example of an arrangement of a conventional image sensing apparatus including a VAP for camera shake correction will be described below with reference to FIG. 15.
In FIG. 15, a VAP 104 is constituted by coupling two glass plates 104a and 104b via a bellows-like spring member 104c and sealing an optically transparent liquid 104d in the space surrounded by the two glass plates 104a and 104b and the spring member 104c. Shafts 104e and 104f provided in the glass plates 104a and 104b are connected to an actuator 103 for horizontal driving and an actuator 108 for vertical driving, respectively. Therefore, the glass plate 104a is rotated horizontally, and the glass plate 104b is rotated vertically.
Note that the VAP 104 is described in Japanese Patent Laid-Open No. 2-12518 and so a detailed description thereof will be omitted.
A horizontal angular velocity sensor 101 detects an angular velocity caused by a horizontal motion of the image sensing apparatus resulting from a camera shake or the like. A control unit 102 performs an arithmetic operation for the detection signal from the angular velocity sensor 101 such that this horizontal motion of the image sensing apparatus is corrected, and detects and supplies an acceleration component to the actuator 103. This actuator 103 drives the glass plate 104a of the VAP 104 horizontally.
The rotational angle of the glass plate 104a which can be horizontally rotated by the actuator 103 is detected by an angle sensor 105. The control unit 102 performs an arithmetic operation for this detected rotational angle and supplies the result to the actuator 103.
A vertical angular velocity sensor 106 detects an angular velocity caused by a vertical motion of the image sensing apparatus resulting from a camera shake or the like. A control unit 107 performs an arithmetic operation for the detection signal from the angular velocity sensor 106 such that this vertical motion of the image sensing apparatus is corrected, and detects and supplies an acceleration component to the actuator 108. This actuator 108 drives the glass plate 104b of the VAP 104 vertically.
The rotational angle of the glass plate 104b which can be vertically rotated by the actuator 108 is detected by an angle sensor 109. The control unit 107 performs an arithmetic operation for this detected rotational angle and supplies the result to the actuator 108.
An image sensing optical system 110 forms an image of an object to be photographed on an image sensor 111. This image sensor 111 is constituted by, e.g., a CCD. A two dimensional solid state CCD is used in conventional image sensing apparatuses such as video cameras. An output from the image sensor 111 is output to a recording apparatus or a television monitor through a signal processing circuit (not shown).
In the conventional image sensing apparatus with the above arrangement, the horizontal and vertical angular velocities caused by a camera shake are detected. On the basis of the angular velocities detected, the actuators move the VAP horizontally and vertically to refract incident light, thereby performing control such that the image of an object to be photographed does not move on the image sensing plane of the image sensor. Consequently, the camera shake is corrected.
On the other hand, with recent spread of image sensing apparatuses, an increasing demand has arisen for a higher image quality. To meet this demand, it is being attempted to increase the number of pixels of an image sensor such as a CCD in an image sensing apparatus or to develop a high-speed I/O apparatus or an image information compressing/decoding apparatus.
For example, the number of pixels of a conventional two-dimensional solid state CCD is normally 400,000, and the number of pixels of even a high-resolution CCD is at most 2,000,000. These pixel numbers currently available are unsatisfactory to obtain a sufficient resolution necessary for images, hard copies, and computer graphics to be displayed on large screens.
The following methods, therefore, are disclosed as a method of realizing a high image quality with a limited number of pixels of an image sensor.
(1) A method in which an image of an object to be photographed is divided by a prism and photographed by a plurality of image sensors, as found in some presently available video camera recorders.
(2) A method as proposed in, e.g., Japanese Patent Laid-Open No. 60-250789, in which an image region of a photographing optical system is split by, e.g., a secondary imaging optical system, and the individual split regions are photographed by a plurality of image sensors and then synthesized.
(3) A method of pixel shift proposed in, e.g., Japanese Patent Publication Nos. 50-13052, 59-18909, and 59-43035. In this method, an element for splitting a light beam, such as a dichroic mirror or a half mirror, is arranged on the image plane side of an image sensing optical system, and a plurality of area sensors are arranged to be shifted from each other by an amount corresponding to a half pixel pitch or smaller. In this method it is possible to obtain, from a plurality of resulting images, information containing pixels in a number larger than the number of pixels of the area sensors. Also, xe2x80x9cHighvision ⅔-inch compact CCD camera using dual green methodxe2x80x9d in Television Society Magazine, xe2x80x9cImage Information Engineering and Broadcasting Technologyxe2x80x9d, Vol. 47, No. 2, 1993 has reported a method in which two of three CCDs for receiving separated light beams from a trichromatic separation prism are arranged such that their pixels are shifted from each other. In this method an object to be photographed is photographed with this pixel-shifted arrangement.
(4) Japanese Patent Publication No. 57-31701 or 64-863 has disclosed a method by which a pixel shift is performed by moving the position of incident light to an image sensor relative to the image sensor in synchronism with the read timing of an output electrical signal from the sensor. This is accomplished by, e.g., inserting a birefringence polarizing element into a photographing optical system and controlling the element. By periodically photographing the resulting images, it is possible to obtain information containing pixels in a number larger than the number of pixels of the image sensor. Research and development of this pixel shifting method have been made extensively to date.
As discussed above, the camera shake preventing function and the resolution increasing function have been developed in conventional image sensing apparatuses. Unfortunately, in these conventional image sensing apparatuses the camera shake preventing function and the resolution increasing function are independent of each other. Therefore, the conventional image sensing apparatuses must have independent arrangements to include both of the two functions. An image sensing apparatus including both these functions, therefore, is difficult to manufacture at a low cost and miniaturize.
In addition, in a conventional image sensing apparatus which realizes a high-resolution by using the pixel shifting method as described above, this pixel shifting function and various other automatic adjusting functions of the image sensing apparatus may interfere with each other, thereby causing a function failure. As an example, if a pixel shift is performed by slightly vibrating a focusing lens group or an image sensor in the optical axis direction while an automatic focusing device is operating using TV signal AF (Auto Focus), no stable peak value output of a luminance signal can be obtained. This degrades the original performance of the automatic focusing device. Also, if a pixel shift is done while another automatic adjusting device is in operation, out-of-focus images or over exposed-images result in some cases. In addition, if a pixel shift is performed during zooming, the moving amount of the position of incident light to an image sensor cannot be held constant. Consequently, it may become impossible to obtain a satisfactory image quality.
Furthermore, since a pixel shift is done although no satisfactory effect can be expected, the resolution increasing function operates unnecessarily, consuming an extra power. This is especially a serious problem in portable image sensing apparatuses in which power is supplied by a battery.
It is an object of the present invention to provide an image sensing apparatus including both of a camera shake preventing function and a resolution increasing function with a simple arrangement.
According to the present invention, the foregoing object is attained by providing an image sensing apparatus comprising image forming means for forming an image of an object to be photographed, image sensing means for photographing the image of the object formed by the image forming means, displacing means for displacing the image of the object formed by the image forming means and the image sensing means relative to each other, and control means for performing switching between a first image sensing mode in which the displacing means performs a vibration correction to yield a low resolution image and a second image sensing mode in which the displacing means performs a pixel shift to yield a high-resolution image.
In accordance with the present invention as described above, the first or second image sensing mode is selected either arbitrarily by a user or automatically. Consequently, when dynamic images are required, information of dynamic images free from a blur can be obtained by moving the relative positions of an image of an object to be photographed, which is formed by an optical system, and an image sensor by an amount by which a camera shake is corrected. When a high-resolution is necessary, the relative positions of the image of the object formed by the optical system and the image sensor are finely moved to photograph a plurality of images, and these images are synthesized.
It is another object of the present invention to provide an image sensing apparatus capable of properly determining whether a resolution increasing function is to be executed, thereby enhancing a power-saving effect.
According to the present invention, the foregoing object is achieved by providing an image sensing apparatus comprising image forming means for forming an image of an object to be photographed, image sensing means for photographing the image of the object formed by the image forming means, displacing means for displacing the image of the object formed by the image forming means and the image sensing means relative to each other, synthesizing means for obtaining a high-resolution image by synthesizing a plurality of images of the object obtained by performing a pixel shift by the displacing means, changing means for changing photographing conditions, and control means for determining, in accordance with the photographing conditions changed by the changing means, whether the displacing means is to be driven.
In accordance with the present invention as described above, driving of the displacing means for performing a pixel shift can be controlled in accordance with the photographing conditions. Consequently, an unnecessary pixel shift is not performed.
It is another object of the present invention to provide an image sensing apparatus capable of further increasing the resolution by using an image sensor with a limited number of pixels.
According to the present invention, the foregoing object is attained by providing an image sensing apparatus comprising image forming means for forming an image of an object to be photographed, image sensing means for photographing the image of the object formed by the image forming means, displacing means for displacing the image of the object formed by the image forming means and the image sensing means relative to each other, synthesizing means for obtaining a high-resolution image by synthesizing a plurality of images of the object obtained by performing a pixel shift by the displacing means, and vibration correcting means for selectively performing a vibration correction by using the displacing means.
In accordance with the present invention as described above, the resolution can be further increased in addition to being able to perform a vibration correction.
The invention is particularly advantageous since there can be provided an image sensing apparatus by which an image recording mode is selected either arbitrarily by a user or automatically, and so it is possible to selectively obtain low resolution images free from a blur caused by a vibration such as a camera shake and high-resolution images. Since these two types of images are formed by using a common arrangement, the configuration of the image sensing apparatus is exceedingly simplified.
In addition, whether the resolution increasing function is to be executed is properly determined. Consequently the power-saving effect is enhanced, and the resolution increasing function is prevented from having an adverse influence on other operations of the apparatus.
Furthermore, since a high-resolution can be realized by using a conventional camera shake preventing device, a larger amount of a high-frequency component can be detected. This makes an accurate focus detection feasible.